In general, the fundamental steps for processing a color light-sensitive material are the color developing step and the desilvering step. In the color developing step, exposed silver halide is reduced with a color developing agent to generate silver and the oxidation developing agent reacts with a coupler to form a dye image. In the subsequent desilvering step, silver formed in the developing step is oxidized by the action of an oxidizing agent generally called a bleaching agent and is then dissolved with an agent for forming a complex ion of a silver ion, which is generally called as a fixing agent. After going through this desilvering step has been performed, only the dye images are formed on the color light-sensitive material.
Usually, after these steps, a washing processing is carried out to remove an unnecessary processing solution drainage.
In the case of a color paper and a reversal color paper, the processing is finished with the above steps and a drying step generally follows. In the processing of a color negative film and a reversal color film, a stabilizing step is necessary in addition to the above steps. It is well known that the stabilizing bath in the final step following these processing steps contains formaldehyde for the purpose of preventing fading of the magenta dye attributable to the magenta coupler remaining in the light-sensitive material after processing. A small quantity of formaldehyde vapor is generated when the stabilizing bath containing formaldehyde is prepared and a light-sensitive material having a stabilizing solution attached thereon is dried.
It is known that the inhalation of formaldehyde is harmful for the human body and the Japan Association of Industrial Health advises that the allowable concentration of formaldehyde in a working environment is 0.5 ppm. Therefore, the effort to reduce the concentration of formaldehyde in the stabilizing bath and replace formaldehyde with an alternative has been made to improve the working environment.
A hexamethylenetetramine compound is described in, for example, JP-A-63-244036 (the term "JP-A" as used herein means an unexamined published Japanese patent application), as an alternative for formaldehyde. The use of this compound reduces the concentration of formaldehyde, that is, the vapor pressure of formaldehyde, but it also restricts the desired anti-fading function of a magenta dye and causes a marked fading within several weeks even at room temperature.
On the other hand, many N-methylol compounds having the specific structure have been proposed. For example, U.S. Pat. Nos. 2,487,569 and 2,629,660 disclose N-methylol compounds of melamines; U.S. Pat. No. 2,579,435 discloses N-methylol compounds of urea or 2-oxapropylene urea; U.S. Pat. No. 2,487,446 and JP-B-45-8506 disclose N-methylol compounds of thiourea compounds; U.S. Pat. No. 2,579,436 and British Patent No. 684,540 disclose N-methylol compounds of hydantoins; British Patent No. 908,136 discloses N-methylol compounds of cyandiamides; U.S. Pat. No. 3,801,322 and JP-A-61-35447 disclose N-methylol compounds of guanidines; British Patent 1,392,134 discloses N-methylol compounds of morpholine or biuret compounds; and JP-A-2-153348 discloses N-methylol compounds of pyrrole, pyrrolidine, methylamine, glycine, or ethylcarbamate. Further, the methods for using these compounds have also been proposed in, for example, U.S. Pat. No. 4,786,583, 4,859,574, and 4,921,779 and European Patents No. 345,172A and 395,442A.
However, of these compounds, those having the reduced vapor pressure of formaldehyde as compared with formaldehyde itself are poor in the image preservability, and those having the improved image preservability only have the same vapor pressure of formaldehyde as formaldehyde itself. These compounds can not have both the effect of improving the image preservability and the reduction of vapor pressure of formaldehyde.
Also, it has been found that these compounds cause the formation of stain, the deterioration of preservability of a yellow or cyan dye or other dyes contained in the light-sensitive material, and the reduction of solubility although the image preservability of a magenta dye is improved, and there is the problem that these compounds stick to the light-sensitive material and stain the processed image.
Therefore, there has been a strong demand for a compound having a sufficient anti-fading function to a magenta dye and the low formaldehyde vapor pressure, that is, for an effective alternative for formaldehyde.